Optical filters have been used in glazings in window technology to control the flow of light and heat through the glazing. Such filters may be used on any sort of window, including those in buildings, vehicles, aircraft, spacecraft, ships or the like. Optical filters have also been used to regulate lighting and heating levels, for glare reduction, and energy load management. As an example, buildings consume over one third of all energy and over two thirds of the electricity used in the United States, and are responsible for about one third of all greenhouse gas (GHG) emissions, as well as about 30% of a building's energy loss. As such, windows with improved technology for reducing heat loss and solar heat gain can offer significant benefits and cost savings.
Optical filters have also found application in ophthalmic devices to control the amount of light impacting the eye. Opthalmic applications include, for example, prescription and non-prescription glasses, goggles, sunglasses, visors, and safety eyewear.
In order to dynamically control the flow of light and heat through an optical filter, there are a number of technologies that have been used in optical filters, and related devices and applications, including photochromics, electrochromics, liquid crystals, thermochromics, and suspended particle displays. In particular, electrochromic, liquid crystal, and suspended particle displays or devices tend to alternate between dark and light operating states (or transmissive states) in response to electricity. Electrochromic optical filters, for example, tend to darken when a voltage differential is applied across a pair of terminals electrically coupled to different sides of the electrochromic material, and tend to lighten when the polarity of the voltage differential is reversed. On the other hand, photochromic displays or devices tend to automatically darken when exposed to sunlight or UV, and lighten in the absence of sunlight or UV through a thermal back reaction.
It is known that repeated switching of an optical filter from one state of light transmissibility to another state of light transmissibility can cause the optical filter to degrade over time. In particular, the electrical stability and durability of such devices can be worsened through extensive switching of the optical filter, resulting in a filter whose light transmissibility reduces over time. Attempts have therefore been made to improve the electrical stability and durability of switchable optical filters, to thereby increase their lifetime of usability. The current disclosure describes an improved layered transparent electrode structure that may be used in variable transmission switchable optical filters, and that increases their electrical stability and durability.